Armature-commutator assembly and method of assembling an armature-commutator

ABSTRACT

An armature-commutator assembly and method of assembling an armature-commutator of a type formed of ferromagnetic lamina or sheet metal plates having slots defined by radially extending teeth with a hole extending axially through each tooth of each lamina. The axially extending holes in each tooth of the assembled armature lamina providing a longitudinally extending channel opening in which an insulating tubing may be inserted so as to extend therethrough for receiving therein a shank or stem portion of a commutator bar. In assembling the armaturecommutator, the stem portion of each of the commutator bars are initially only partially inserted into the insulating tubing in the channel holes in the commutator teeth so that appropriate connections may be then made between electrical terminal ends of coil windings wound in the slots of the armature defined by the radially extending teeth of the armature. The stem portions of the commutator bars thereafter are fully inserted into the insulating tubing in the channel holes in the armature teeth with projecting head portions of the commutator bars being provided at free end portions of the bars so as to form an effective commutator surface at one end of the armature assembly. The armature-commutator assembly is then potted and machined to meet the requirements of the dynamoelectric machine in which the same is to be utilized.

United States Patent [72] Inventor George Frank Cupsaw Lake, NJ. [21]Appl. No. 4,254 [22] Filed Jan. 20, 1970 [45] Patented Feb. 9, 1971 [73]Assignee The Bendix Corporation a corporation of Delaware [54]ARMATURE-COMMUTATOR ASSEMBLY AND METHOD OF ASSEMBLING AN ARMATURE-COMMUTATOR 7 Claims, 8 Drawing Figs.

[52] U.S.Cl 310/234, 29/596, 310/236, 310/216, 310/42 [51] Int. Cl H02k[50] Field ofSearch 310/233, 4, 5, 6, 216, 42; 29/596, 597, (lnquired)[5 6] References Cited UNITED STATES PATENTS 1,631,186 6/1927 Apple3l0/235X 2,298,862 10/1942 Balz et a1. 310/233X 2,756,354 7/1956 Baron310/43 2,861,203 11/1958 Luneau et a1. 310/40 Primary Examiner-D. X.Sliney Atr0rneysHerbert L. Davis and Plante, Arens, l-lartz, Smith andThompson ABSTRACT: An armature-commutator assembly and method ofassembling an armature-commutator of a type formed of ferromagneticlamina or sheet metal plates having slots defined by radially extendingteeth with a hole extending axially through each tooth of each lamina.The axially extending holes in each tooth of the assembled armaturelamina providing a longitudinally extending channel opening in which aninsulating tubing may be inserted so as to extend therethrough forreceiving therein a shank or stem portion of a commutator bar. Inassembling the armature-commutator, the stem portion of each of thecommutator bars are initially only partially inserted into theinsulating tubing in the channel holes in the commutator teeth so thatappropriate connections may be then made between electrical terminalends of coil windings wound in the slots of the armature defined by theradially extending teeth of the armature. The stem portions of thecommutator bars thereafter are fully inserted into the insulating tubingin the channel holes in the armature teeth with projecting head portionsof the commutator bars being provided at free end portions of the barsso as to form an effective commutator surface at one end of the armatureassembly. The armature-commutator assembly is then potted and machinedto meet the requirements of the dynamoelectric machine in which the sameis to be utilized.

' SHEET 2 OF 4 FIG. 2

INVENTOR.

GEORGE F/PA/V ArroA VEY PATENTEDFEB 9m: I 3,562,570

SHEET 3 BF 4 FIG. 3

FIG. 4

INVENTOR. GEORGE PR4 K ATTORNEY PATENT-Ema 91971 I 3.562.570

saw u 0F 4 3o 32 as 0 I INVENTOR. GEORGE FRANK ARMATURE-COMMUTATORASSEMBLY AND METHOD OF ASSEMBLING AN ARMATURE-COMMUTATOR BACKGROUND OFTHE INVENTION 1,. Field of the Invention A compact armature-commutatorassembly in which the armature teeth include means for supporting stemportions of commutator bars having projecting head portions which may bemachined to form a commutator surface at one end of the armature of adynamoelectric machine.

2. Description of the Prior Art The invention relates to improvements inan armature-commutator assembly and to an improved method of assemblingan armature-commutator for utilization in a dynamoelectric machine of atype such as disclosed in a U.S. Pat. No. 2,298,862, granted Oct. 13,1942 to Harry W. Ball and Lawrence F. Hemphill for a DynamoelectricMachine Construction" and to improvements in an armature-commutatorassembly and method of assembling an armature-commutator structure forutilization in a dynamoelectric machine of a type such as disclosed in aU.S. Pat. No. 2,861,203, granted Nov. 18, [958 to John R. Luneau andChristian H. H. U'nruh for a torquer.

In the structures disclosed by both of these patents there are utilizedcoil receiving slots defined by the teeth of the armature structure forreceiving the'stem or shank of commutator bars with the head portions ofthe bars being so arranged as to form the commutator of the motorstructure.

However in the arrangement disclosed by the aforenoted patents while thespace in the slots between the armature teeth are utilized to receivethe so-called shank of the bars of the commutator, the resultant loss ofslot area and concomitant loss of armature copper of the coil windingsreceived therein may inherently effect a severe degrading in the outputcharacteristics of the structure of the dynamoelectric machine disclosedby such patents.

Furthermore, in a U.S. Pat. No. 2,756,354 granted July 24, 1956 to R. M.A. Baron for Armatures of Electric Motors" there has been disclosedanother arrangement in which commutator rods are embedded in anelectrical insulating core moulded in a central bore formed in stackedlamina of the armature assembly of the disclosed dynamoelectric machine.Such arrangement, however, is not readily adaptable to an electric motorof the minute size to which the present invention is particularlydirected.

Furthermore the provision of a core of an electrically insulatedmaterial within an axial bore formed in ferromagnetic stack sheetstampings of an armature assembly, such as disclosed in the Baron U.S.Pat. No. 2,756,354, may also effect a concomitant loss of armature ironto in turn effect a severe degrading of output characteristics of thedynamoelectric machine utilizing such an armature-commutator assembly aswell as provide an armature-commutator assembly which is not subject tothe ease and expediency of assembly of that of the armature-commutatorof the present invention.

The present invention rests in a conception which simplifies theassembly and methodof assembly of a dynamoelectric machine of minutesize in the stamping of the lamina for forming the armature assembly ofthe machine with separate openings in the teeth of each lamina so as toprovide channel openings in the teeth of an assembled lamina stackedcore of the armature assembly for receiving stem portions of commutatorbars, while at the same time the assembly and method of assembly of thepresent invention is such as to raise the percent of durability andcertainty of operation of the machine of such minute size so as toeffect a condition of greater durability and one which is more sure toproduce the desired result in emergency and not only with greatercertainty but with less expense.

SUMMARY OF THE INVENTION As distinguished from the structuralarrangement and method of assembly disclosed in the aforenoted patents.the present invention contemplates the provision of separate openingsformed in each ofthe teeth ofthe armature lamina at the time of theinitial stamping of the lamina of a ferromagnetic sheet metal material.Thereafter the stamped sheetmetal lamina are assembled in the form ofacylindrical core with the stamped openings in the teeth positioned in acorresponding axially aligned relation so as to provide channel openingsextending axially in the cylindrical core of the armature assembly inparallel relation for receiving therein tubular insulating elements inwhich may be received stem or shank portions of the several commutatorbars. Each of the commutator bars having head portions at outer ends ofthe bars so arranged as to form a commutator assembly at one end of thecylindrical armaturecore within a predetermined overall axial length, aswell as overall diameter of the armature.

The invention contemplates as another object, the provision of a novelarmature-commutator assembly for a dynamoelectric machine including acylindrical core of a ferromagnetic material, the core having an axis ofrotation and transverse slots in a cylindrical surface thereof, saidslots defined by radially extending teeth, each of the teeth of thearmature structure including axially extending openings therein forreceiving insulated stem or shank elements of commutator bars, and whichstem or shank elements serve as electrical leads from coil windingsmounted in the slots defined by the teeth of the armature with coil endsextending beyond the ends of the slots in an arrangement in whichcommutator head portions of the commutator bars are effectively mountedwithin the overall axial length of the armature determined by the coreand the coil ends extending therefrom as well as within the overalldiameter of the armature determined by the radius between saidcylindrical surface and the axis of rotation of the core.

Another object of the invention is to provide an improved method ofassembling the foregoing armature-commutator structure in whichlaminations of ferromagnetic sheet metal material may be stamped with aplurality of axially extending teeth defining therebetween slots forreceiving armature winding coils of a dynamoelectric machine and inwhich each of the teeth of the stamped sheet metal lamina havingopenings stamped therein in close proximity to the circumferential edgesurface of each lamina. The sheet metal lamina being thereafter stackedin a core assembly with teeth defining slots and with the openings inthe teeth in a corresponding axial alignment so as to provide channelopenings extending in parallel longitudinal relation through the core.Armature winding coils may be thereafter received in the slots'of theassembled core for electrical connection thereafter at suitableelectrical terminals to a stem or shank portion of each of thecommutator bars formed of an electrically conductive material. Prior toassembly of the commutator bars in the core, there are inserted into theaxially extending channel openings in the teeth of the armature tubularelectrical insulating elements. Thereafter a stem or shank portion of acommutator bar is partially inserted in each of the tubular elements soas to be electrically insulated from the armature lamina. Each stemportion is then electrically connected to suitable electrical ter-,minals of the armature winding coils and thereafter the stem portionsare fully inserted into the tubular insulating elements in the axiallyextending channel openings formed in the teeth of the armature core witha head portion of each of the commutator bars being positioned adjacentto and electrically insulated from an end surface of the stackedarmature core by a sheet of insulating material and positioned in closeproximity to the circumferential surface of the stacked armature laminacore assembly ,and in close proximity to the axial limit of the lengthof the armature assembly, as defined by the armature core and ends ofthe armature winding coils extending from the ends of the slots formedin the core.

These and other objects and features of the invention are pointed out inthe following description in terms of the embodiment thereof which areshown in the accompanying drawings. It is to be understood, however,that the drawings are for the purpose of illustration only and are not adefinition of the limits of the invention. Reference is to be had to theappended claims for this purpose.

DESCRIPTION OF THE DRAWINGS In the drawings corresponding numeralsindicate corresponding parts in the several views:

FIG. 1 is an enlarged end view of a dynamoelectric machine embodying theimproved armature-commutator assembly of the present invention andshowing a typical brush supporting structure in cooperative relationwith the commutator.

FIG. 2 is a sectional view of FIG. 1 taken along the lines 2-2 andlooking in the direction of the arrows.

FIG. 3 is an end view of a core of an armature lamina assembly formed ofsheet metal plates of a ferromagnetic material with the armaturewindings removed and illustrating an improved arrangement embodying thepresent invention in the provision of insulating tubing in channelopenings formed in teeth of the lamina for receiving stem portions ofthe commutator bars shown in the enlarged views of FIGS. 1 and 2.

F IG'. 4 is a sectional view of FIG. 3 taken along the lines 4-4 andlooking in the direction of the arrows so as to show the arrangement ofthe insulating tubing in a channel opening and discs of electricalinsulating material at opposite end surfaces of the armature core.

FIG. 5 is an end view illustrating the detailed structure of a sheetmetal plate of the annature lamina and illustrating the openings formedin the teeth of the lamina in close proximity to the circumferentialedge surface thereof.

FIG. 6 is an end view of the armature lamina of FIG. 5.

FIG. 7 is a top plan view of a commutator bar.

FIG. 8 is a side view of the commutator bar shown by FIG. 7.

DESCRIPTION OF THE INVENTION In the present invention, as shown by FIGS.1 and 2, the improved armature structure 10 is applied to adynamoelectric machine indicated generally by the numeral 12. Thearmature 10 may include a core assembly 13 of a plurality of lamina ofsheet metal plates 14 of a ferromagnetic material and one of which isindicated in detail at FIGS. 5 and 6.

The plates 14 include a plurality of radially extending teeth 16defining therebetween radial slots 18 for receiving therein suitablearmature winding coils 20, as shown by FIGS. 1 and 2,

formed of electrical conductors arranged in the winding slots 18 of thecore assembly 13 of the armature 10. The lamina or sheet metal plates 14of the armature 10 are formed of a suitable ferromagnetic materialhaving a concentric circular opening 21. The assembled core 13 of thearmature 10 may be mounted on a shaft 22 which may project-through thecircular openings 21 in the assembled parts of the core 13 and berotatably positioned in a suitable bearing 24. The shaft 22 is arrangedin concentric relation to a magnetic ring 26 of the dynamoelectricmachine 12.

Each of the adjacent radial teeth 16 of the lamina or sheet metal plates14, as shown in FIG. 5 include lip portions 28 overhanging and partiallyclosing the radial openings into the slots 18 for retaining the coils inthe slots 18.

A feature of each of the lamina or sheet metal plates 14 is an opening30 which may be stamped in each of the teeth 16 adjacent the overhanginglip portions 28 of the openings 30 and simultaneously with the stampingof the slots 18 and in close proximity to the circumferential edgesurface 32 of the lamina or sheet metal plate 14.

In the assembly of the core 13 of the armature 10, a plurality of thelamina sheet metal plates 14 are stacked with the teeth 16, slots 18,concentric openings 21 and openings 30 of the several plates 14 arrangedin axial alignment. The stack of lamina or sheet metal plates 14 formthe core 13 of the armature l0 and may be then suitably secured in thealigned position.

There is then secured adjacent each outer surface 37 of the end laminaplate 14, as shown in FIGS. 2 and 4. a disc 39 formed of an electricalinsulating material and of a shape corresponding to that of the endsurface 37 of the lamina 14. Each of the discs 39 are also formed withopenings 34, 36 and 38 correspondingly located, respectively, to theslots 18 and openings 30 and 21 in the end lamina 14, as shown in FIG.3. A tubular element 35 of an electrical insulating material is theninserted in each of the longitudinal channels formed by the alignedopenings 30 in the teeth 16 and corresponding openings 34 in the disc39, as shown by FIGS. 2, 3 and 4. The tubular insulating element 35 istrimmed flush with the outer surface of the discs 39 at opposite ends ofthe core 13.

Following the assembly of the stacked lamina l4 and insulation discs 39,the coils 20 of the electrical armature windings are received in theslots 18 in a conventional manner and held in place in the slots 18 bythe overhanging lip portions 28 of the teeth 16.

The stem portions 40 of the commutator bars 42 are then partiallyinserted into each of the insulating tubes 35. The stem portion 40 ofthecommutator bar 42 and the head portion 45 are shown in detail by FIGS. 7and 8. The commutator bar 42 is formed of a suitable electricalconducting material and has the head portion 45 which projectssubstantially from the stem portion 40 andbeyond the core I3 of thearmature 10. The coils 20 of the electrical armature windings are soformed as to provide suitable clearance for the commutator heads 45.Suitable electrical insulating material 46 is provided to electricallyinsulate the coil windings 20 from the commutator heads 45. Appropriateelectrical connections are then made as by soldering suitable electricalterminals of the coils 20 of the armature windings to a part of the stemportions 40 of the commutator bars 42 that is exposed from the tube 35.

After the electrical connections have been made to the commutator bars42, the stem portions 40 thereof are then fully inserted into theinsulated tubings 35 positioned in the longitudinal channels formed bythe openings 30 in the lamina 14 of the core assembly 13 with the headportions 45 of the commutator bar 42 in each case being positionedimmediately adjacent an outer surface of the electrical insulationlamina or disc 39, as best shown in FIG. 2. The armature-commutatorassembly may then be potted with a suitable electrical insulatingplastic material and machined to meet operational requirements.

In the assembly of the commutator-armature structure 10 of FIGS. 1 and 2the commutator bars 42 must be rigidly fixed in place in order to serveas an effective commutator. Accordingly the openings 30, as shown byFIGS. 3 and 5, in the armature teeth 16 of the lamina or sheet metalplates 14 together with the insulating tubing 35 act to hold the stemelements 40 and the head portions 45 in place so as to provide thecommutator structure 42, as shown in FIGS. 1 and 2, with suitable brushelements 50 biased under spring tension of a leaf spring 52. In additiona suitable electrical insulating plastic or potting material fills thespacing in the openings 30 so that when cured the potting materialcompletely immobilizes the commutator bars 40.

Furthermore the shape of the openings 30 in the armature teeth 16 andthe corresponding shape of the shank or stem elements 40 of thecommutator bar 42 may vary with the shape of the armature tooth 16. Thuswhile a rectangular shape of the opening 30 is shown in the assemblydescribed with reference to FIGS. 1, 2, 3 and 5 it may be readily seenthat other shapes as determined by tooth flux density, tooth crosssection and other factors may be used as long as rotation of the stemelement 40 of the bar is prevented. Some other effective shapes of theopening 30 would be square, triangular and trapezoidal. The shape of theinsulation tubing 35 between the stem element 40 of the commutator bar42 and the armature opening 30 may also vary with any particular designas determined by environmental limits, availability or particular sizesand other factors.

From the foregoing it will be seen that there has been provided anarmature-commutator structure with insulated openings in the armatureteeth so shaped that properly shaped stem elements 40 of commutator bars42inserted therein cannot move, while the whole of the armaturecommutator assembly when potted or impregnated with a suitableinsulating plastic material acts as an armature-commutator assembly asbest shown in FIGS. 1 and 2. Moreover in the aforenoted assembly thereis provided a method for incorporating a commutator within the overallaxial length and overall diameter of the armature structure 10, as bestshown in FIGS. 1 and 2.

lclaim:

1. An armature for a dynamoelectric machine, the armature being of atype including a cylindrical core of a ferromagnetic material, said corehaving an axis of rotation and transverse slots in a cylindrical surfacethereof, said slots being defined by radially extending teeth of saidcore, said teeth having portions overhanging and partially closing saidslots, the cylindrical core having a radius between said cylindricalsurface and the axis of rotation of the core determining an overalldiameter of the armature, winding coils in said slots and having coilends extending beyond said slots, and said coil ends and said coredetermining an overall axial length of the armature; the improvementcomprising each of said radially extending teeth of the core having achannel extending longitudinally through said overhanging portion of thetooth in a parallel relation to said transverse slots and in closeproximity to said cylindrical surface of the core, electricallyconductive commutator bars, each of said commutator bars including astem portion and a head portion, the stem portion of each of saidcommutator bars being positioned in a different one of saidlongitudinally extending channels and electrically connected to saidwinding coils, first means positioned in said longitudinally extendingchannels to electrically insulate the stem portions of said com mutatorbars from the core, the head portion of each of the commutator barsoverlying said coil ends within said overall diameter and within saidoverall axial length of said armature, the head portions of saidcommutator bars serving as commutator segments, and second means affixedto an outer end surface of said cylindrical core to electricallyinsulate the head portions of the commutator bars from the outer endsurface of the cylindrical core.

2. The improvement defined by claim 1 in which the first means includestubular elements of electrical insulating material positioned in each ofsaid longitudinally extending channels to electrically insulate the stemportions of said commutator bars from the core, and in which the secondmeans includes a disc of an electrical insulating material affixed tothe outer end surface of the cylindrical core to electrically insulatethe head portions of the commutator bars from the outer end surface ofthe cylindrical core.

3. ln assembling an armature-commutator of a type including acylindrical core of a ferromagnetic material, said core having an axisof rotation and transverse slots in a cylindrical surface thereof, saidslots being defined by radially extending teeth of said core; animproved method of assembling the cylindrical core, including the stepsof providing a plurality of metal plates, each of said plates being of aferromagnetic material, forming said metal plates with radiallyextending teeth defining slots therebetween, forming each of said teethwith an opening therethrough in close proximity to a circumferentialedge of the plate, stacking said plates so as to assemble thecylindrical core with the teeth, slots and openings in a correspondingrelation so that the corresponding openings form longitudinallyextending channel openings through the teeth of the core, thelongitudinal channel openings extending in parallel relation to theslots defined by the teeth of the core. winding coils in said slots,partially inserting stem portions of electrically conductive commutatorbars into the longitudinally extending channel openings with parts ofthe stem portions of the commutator bars being exposed from the channelopenings, electrically connecting said winding coils to the exposedparts of the stem portions of the electrically conductive commutatorbars, and thereafter fully inserting the stem portions of the commutatorbars into the channel openings extending longitudinally through theteeth of the core with head portions of the commutator bars projectingfrom one end surface of the cylindrical core so as to provide aneffective commutator surface.

4. The improved method of assembling the cylindrical core defined byclaim 3 including the step of inserting into each of the longitudinallyextending channel openings an electrical insulating element to insulatethe stem portions of the electrically conductive commutator bars fromthe plates of the assembled core.

5. The improved method of assembling the cylindrical core defined byclaim 3 including the step of affixing to an end surface of theassembled core an electrical insulating disc to insulate the headportions of the commutator bars from the end surface of the assembledcore.

6. The improved method of assembling the cylindrical core defined byclaim 5 including the step of inserting into each of the longitudinallyextending channel openings an electrical insulating element to insulatethe stem portions of the electrically conductive commutator bars fromthe plates of the as sembled core.

7. The improved method of assembling the cylindrical core defined byclaim 3 including the steps of affixing to the one end surface of theassembled core an electrical insulating disc having openings thereincorresponding positioned to the openings in the teeth of the assembledcore, thereafter inserting through said openings in the insulating discand into each of the channel openings extending longitudinally throughthe teeth of the core a tubular electrical insulating element, and thentrimming an end of each tubular insulating element flush with an outersurface of the electrical insulating disc preparatory to a later partialinsertion of the stem portions of the com-

1. An armature for a dynamoelectric machine, the armature being of atype including a cylindrical core of a ferromagnetic material, said corehaving an axis of rotation and transverse slots in a cylindrical surfacethereof, said slots being defined by radially extending teeth of saidcore, said teeth having portions overhanging and partially closing saidslots, the cylindrical core having a radius between said cylindricalsurface and the axis of rotation of the core determining an overalldiameter of the armature, winding coils in said slots and having coilends extending beyond said slots, and said coil ends and said coredetermining an overall axial length of the armature; the improvementcomprising each of said radially extending teeth of the core having achannel extending longitudinally through said overhanging portion of thetooth in a parallel relation to said transverse slots and in closeproximity to said cylindrical surface of the core, electricallyconductive commutator bars, each of said commutatoR bars including astem portion and a head portion, the stem portion of each of saidcommutator bars being positioned in a different one of saidlongitudinally extending channels and electrically connected to saidwinding coils, first means positioned in said longitudinally extendingchannels to electrically insulate the stem portions of said commutatorbars from the core, the head portion of each of the commutator barsoverlying said coil ends within said overall diameter and within saidoverall axial length of said armature, the head portions of saidcommutator bars serving as commutator segments, and second means affixedto an outer end surface of said cylindrical core to electricallyinsulate the head portions of the commutator bars from the outer endsurface of the cylindrical core.
 2. The improvement defined by claim 1in which the first means includes tubular elements of electricalinsulating material positioned in each of said longitudinally extendingchannels to electrically insulate the stem portions of said commutatorbars from the core, and in which the second means includes a disc of anelectrical insulating material affixed to the outer end surface of thecylindrical core to electrically insulate the head portions of thecommutator bars from the outer end surface of the cylindrical core. 3.In assembling an armature-commutator of a type including a cylindricalcore of a ferromagnetic material, said core having an axis of rotationand transverse slots in a cylindrical surface thereof, said slots beingdefined by radially extending teeth of said core; an improved method ofassembling the cylindrical core, including the steps of providing aplurality of metal plates, each of said plates being of a ferromagneticmaterial, forming said metal plates with radially extending teethdefining slots therebetween, forming each of said teeth with an openingtherethrough in close proximity to a circumferential edge of the plate,stacking said plates so as to assemble the cylindrical core with theteeth, slots and openings in a corresponding relation so that thecorresponding openings form longitudinally extending channel openingsthrough the teeth of the core, the longitudinal channel openingsextending in parallel relation to the slots defined by the teeth of thecore, winding coils in said slots, partially inserting stem portions ofelectrically of electrically conductive commutator bars into thelongitudinally extending channel openings with parts of the stemportions of the commutator bars being exposed from the channel openings,electrically connecting said winding coils to the exposed parts of thestem portions of the electrically conductive commutator bars, andthereafter fully inserting the stem portions of the commutator bars intothe channel openings extending longitudinally through the teeth of thecore with head portions of the commutator bars projecting from one endsurface of the cylindrical core so as to provide an effective commutatorsurface.
 4. The improved method of assembling the cylindrical coredefined by claim 3 including the step of inserting into each of thelongitudinally extending channel openings an electrical insulatingelement to insulate the stem portions of the electrically conductivecommutator bars from the plates of the assembled core.
 5. The improvedmethod of assembling the cylindrical core defined by claim 3 includingthe step of affixing to an end surface of the assembled core anelectrical insulating disc to insulate the head portions of thecommutator bars from the end surface of the assembled core.
 6. Theimproved method of assembling the cylindrical core defined by claim 5including the step of inserting into each of the longitudinallyextending channel openings an electrical insulating element to insulatethe stem portions of the electrically conductive commutator bars fromthe plates of the assembled core.
 7. The improved method of assemblingthe cylindrical core defined by claim 3 including the steps of afFixingto the one end surface of the assembled core an electrical insulatingdisc having openings therein corresponding positioned to the openings inthe teeth of the assembled core, thereafter inserting through saidopenings in the insulating disc and into each of the channel openingsextending longitudinally through the teeth of the core a tubularelectrical insulating element, and then trimming an end of each tubularinsulating element flush with an outer surface of the electricalinsulating disc preparatory to a later partial insertion of the stemportions of the commutator bars into the tubular electrical insulatingelements, the tubular elements thereafter electrically insulating thestem portions of the electrically conductive bars from the plates of theassembled core upon the stem portions being fully inserted into thechannel openings while the disc electrically insulates the head portionsof the commutator bars from said one end surface of the assembled core.